Not applicable.
1. Field of the Invention
The field of the invention is flexible pipe for conducting petroleum or other fluids subsea or on land and the method of forming same.
2. Description of the Related Art
Conventional bonded flexible pipe is described in American Petroleum Institute document API Specification 17J. These types of pipe are typically used for both xe2x80x9csweetxe2x80x9d and xe2x80x9csourxe2x80x9d service production, including export and injection services. Fluids transported include oil, gas, water and injection chemicals and gas. A typical construction is made up of a plurality of tubular layers, starting with an interlocking metal carcass and followed by a liner tube of plastic to retain the fluid within the pipe. Hoop strength armor reinforcement in the hoop direction is provided by helical metal wires which may be in several layers and wound in opposite helical directions. Additional layers may also be used, with a final jacket extrusion to complete the assembly, with a tough wear resistant material.
U.S. Pat. Nos. 5,261,462 and 5,435,867, both issued to Donald H. Wolfe, et al., are examples of tubular composite pipe in the prior art. Those patents relate to tubular structures having a plastic tube for the fluid conductor, which has an outer layer formed form alternating spirally wound strips of composite and elastomer. It is believed that the prior art composite pipes, such as disclosed in the above patents, have been limited to relatively short commercial lengths, by reason of the method by which such tubular structures have been made.
Typically, composite flexible pipes are made by filament winding, which involves turning the pipe while feeding and moving resin impregnated fibers from bobbins back and forth along the length of the pipe. Such technique limits the length of the reinforced flexible pipe which can be manufactured because of the number of bobbins required for the large number of fibers that are used in each pass. As a practical matter, it was not known how to make relatively long lengths of composite pipe sufficient for subsea use because of such problem.
In single bobbin machines, unloading and reloading time is a function of the time taken to thread each end of the fibers, the number of bobbins, and the time required to replace each bobbin. Also, due to the material payload requirements, a single bobbin-type machine will require each end to travel some distance from its bobbin over rollers, sheaves, eyelets, etc., through the machine to the closing point on the pipe, thus creating a time-consuming task. Because of the hundreds, and even thousands of bobbins, extremely large machines would be required to make a composite reinforced pipe in long lengths by such prior art techniques, consequently, the industry has not had available composite flexible pipes in long lengths suitable for subsea production and well operations. Multiple fiber tows are also not practical for long pipe lengths because of the fiber loading times required.
With the present invention, discrete tapes are first formed from the fibers and resin or the like, so that the tapes are wound on spools which reduces the number of bobbins required as compared to the number of bobbins required for single fiber filaments, whereby it is possible to manufacture long lengths of composite flexible pipe. The tapes are initially formed and then are fed from tape spools rather than the fiber bobbins in the prior art. Also, each tape is composed of a plurality of superimposed thin tape strips formed of predominantly, unidirectional fibers, which are impregnated with an epoxy or other suitable bonding resin which cures with heat, cold, ultraviolet (UV) or other curing methods. The multi-layer tapes are wrapped with a polyethylene or similar plastic or thin metallic strip or covered by thermoplastic extrusion to confine them as a unit together, with bonding adhesive between the tape strips being prevented from escaping from the wrap. Each tape thus made is fed from a tape spool to the tubular core as the tubular core is rotated, or as the spools are rotated relative to the core, which produces helical wraps of each of the tapes on the tubular core in the same or opposite helical directions for reinforcement of the core.